1. Field of the Invention
The present invention relates to an improved vacuum belt feeder device for feeding successive sheets of paper or the like endwise from the top of a stack of sheets. More particularly, the invention relates to such a device in which the vacuum belt moves in a pivotal manner between a generally horizontal sheet acquiring position and a tilted sheet delivery position, whereby the belt lifts the leading end of the top sheet away from the underlying sheet and also flexes the top sheet to insure its separation from the underlying sheet.
2. Description Relative to the Prior Art
Many devices have been developed in the past to feed successive sheets endwise from the top of a stack of sheets, for example, to deliver the sheets one-at-a-time to a printer or copier apparatus. The well known type of such device to which the present invention is directed employs an endless belt to which the top sheet is adhered by vacuum or suction so that orbital movement of the belt moves the sheet endwise. Preferably, the belt holds the leading edge of the top sheet away from the next lower sheet and it is also advantageous that the top sheet be flexed centrally of the stack to further insure the proper separation of that sheet from the underlying sheet.
The following prior art references disclose variation of the general type of sheet feeder device described above:
U.S. Pat. No. 5,090,676 discloses a sheet feeder in which a vacuum belt is located above the topmost sheet of a pile of sheets and that sheet is moved upwardly into contact with the belt by a jet of air blown against the leading edge of the stack. The belt is perforated only in a specific region and the vacuum is controlled by the position of the perforated belt region relative to a plenum chamber. No means are provided for flexing the top sheet except for a sensor device that would appear to be relatively ineffective from the standpoint of sheet separation because of its close proximity to the trailing end of the sheet.
U.S. Pat. No. 4,643,413 discloses a sheet feeder having a belt assembly comprising a plurality of spaced parallel belts located above a stack of paperboard sheets, with continuously evacuated suction chambers confronting the top sheet between the belts. The belt assembly is movable parallel to itself between lowered and raised positions. When the belt assembly is raised, it lifts the top sheet from the stack and the belt is then driven to move that sheet endwise into a nip between a pair of conveyor rolls. However, the sheet being transported is not flexed to insure its separation from the underlying sheet.
U.S. Pat. No. 3,847,383 discloses a sheet feeder in which a belt assembly with a plurality of perforated vacuum belts is mounted with the belts permanently in sloped relation to the uppermost sheet in the sheet stack. Considerable air flow is therefore required to provide enough vacuum to lift and flex the top sheet into contact with the belts, which is cyclically prevented by a movable finger. The flexure region of the top sheet is not established by the vacuum belts, but, rather, by a buffer plate that is located adjacent the rearward or trailing belt rollers or idlers.
U.S. Pat. No. 3,193,282 shows a device for feeding sheets off the bottom of a stack of sheets by means of a vacuum belt that shifts pivotally about the axis of one of the belt support rollers. However, the shifting of the belt does not move the engaged sheet away from the adjacent stack, but moves the belt from an operative position to a position beyond contact with the sheet with which it was engaged.
U.S. Pat. No. 3,787,044 discloses a device for feeding sheets off the top of a stack, wherein a suction roller is lowered into contact with the top sheet and is then raised and rotated to advance the sheet endwise. A spring finger tends to establish a flexure region in the sheet being advanced. The covering and uncovering of the suction openings in the roller controls the up-and-down and rotational movements of the roller.